The present invention relates to a jack device for connecting a headphone to be used on a passenger seat of an airplane, for example, in particular to the structure of contacting parts with a plug.
In recent aircrafts, an entertainment system is installed to provide music and movie entertainment to passengers. In such a system, individual passengers can listen to selected music or movie audio through a headphone installed on each passenger seat.
In order to improve the sound quality of such an entertainment system, noise-reduction type headphones are increasingly used. A noise reduction type headphone is one in which a noise is cancelled with a sound having a phase opposite to that of the noise. Left and right sound signals as well as DC power are supplied to this type of headphones.
In this type of headphones, three single-head plugs each having plural (mainly two) plug poles are normally used. These plugs are inserted into a jack device provided on a passenger seat for connection. A passenger can listen to desired audio through this connection.
FIG. 10 is an external appearance of a jack device for a conventional headphone. As is illustrated in FIG. 11, the jack device comprises case 200 and cable 26 having a connecting member for connection with a central apparatus of an entertainment system. Case 200 comprises upper case 21 and lower case 22 and is provided with three jack sections (23, 24, 25). Of the three jack sections (23, 24, 25), jack section 23 is for supplying DC power, and the other two jack sections (24, 25) are used for left and right sounds. A single-head plug having plural plug poles is inserted into the inlet port of a jack section to a predetermined position. With this, connection of the single-head plug with the jack section is performed. Cable 26 extends out from case 200 for connection with a central apparatus of an entertainment system.
Inside cases 21, 22 of the jack device, substrates 27, 28, 29 are provided for each respective jack sections 23, 24, and 25 as illustrated in FIG. 11. Each of substrates 27, 28, 29 is soldered to corresponding jack sections 23, 24, 25. Lead wires contained in cable 26 are connected to each of the substrates 27, 28, 29.
A single-head plug is inserted into each of the jack sections 23, 24, 25 as described earlier. Each of these plugs has plural plug poles in the direction of insertion.
Referring to FIG. 12 and FIG. 13 and taking jack section 23 as an example, a description will now be given below on the structure of jack section 23 and the plug to be inserted into it. FIG. 12 shows the cross section of jack section 23.
Jack section 23 for supplying DC power comprises:
a. base 34 having opening 34a for insertion of a plug;
b. movable contact piece 31 as a first contact piece with the plug;
c. grounding spring 30 as a second contact piece with the plug;
d. fixed piece 32; and
e. hollow holder 33 for affixing movable contact piece 31, grounding spring 30, and fixed piece 32.
The structure of the other jack sections 24, 25 is approximately the same as the structure of jack section 23 for supplying DC power.
For example, FIG. 13 is an illustration of a state in which single-head plug 50 has been inserted halfway into jack section 23. Plug 50 has plural plug poles (two plug poles in FIG. 13) in the direction of insertion. As illustrated in FIG. 13, plug 50 comprises plug pole 54 as a first plug pole disposed at the front end of the plug, plug 52 as a second plug pole disposed adjacently to plug pole 54, and insulating collar 56 between plug pole 54 and plug pole 52.
When plug 50 is inserted into jack section 23, plug pole 54 is first brought into contact with grounding spring 30. As plug 50 is further inserted, plug pole 54 is brought into contact with movable contact piece 31.
In conventional jack devices of this type, the spacing (DB in FIG. 12) between movable contact piece 31 and grounding spring 30 on the inlet side is relatively small. As a result, as illustrated in FIG. 13, there occurs a case where plug pole 54 on the front end of the plug is simultaneously brought into contact with movable contact piece 31 and grounding spring 30 in the middle of insertion of plug 50, namely, a state in which plug 50 has been inserted halfway. In the event such simultaneous contact occurs, movable contact piece 31 and grounding spring 30 are short-circuited through plug pole 54.
In such a case, if the jack section is one for supplying a relatively small current such as an audio current, no serious trouble is caused. However, if the jack section is for supplying DC power, the following difficulty will be caused.
Short circuit of contact pieces for DC power inside a jack device will cause an overcurrent in a DC power supply unit of a central apparatus of an entertainment system. The overcurrent may trigger a protection circuit in the central apparatus thus causing suspension of system operation, malfunction or a failure.
The present invention addresses the above-described problems and provides a structure in which plural con tact pieces will not short-circuit in the middle of insertion of a plug. It is an object of the present invention to prevent suspension of operation, malfunction, or failure of an apparatus that is directly or indirectly connected to a jack device.
The present invention provides a jack device into which a single-head plug having plural plug poles in the direction of insertion is inserted for connection, and which comprises:
a base having an opening for insertion of a plug;
a first contact piece that is brought into contact with a first plug pole disposed at the front end of the plug;
a second contact piece that is brought into contact with a second plug pole disposed adjacently to the first plug pole; where
the first and the second contact pieces are provided in the direction of plug insertion; and
the spacing between the plug-contacting portion of the first contact piece and the plug-contacting portion of the second contact piece is made approximately equal to or greater than the length in the direction of plug insertion of the first plug pole of the plug.
Also, a hollow holder to which the first and the second contact pieces are affixed has a notch. When a plug is inserted, the second contact piece is pushed down toward the notch. The notch makes it possible to make the outer dimensions of a jack device with the above structure equal to the outer dimensions of a conventional jack device.
According to the above-described structure, the spacing between the two contact pieces is greater than the length of the above first plug pole. Accordingly, there will not occur any case in which the two contact pieces are simultaneously brought into contact with the first plug pole provided at the front end of the plug. Consequently, the two contact pieces will not make a short circuit through the first plug pole in the middle of plug insertion. Also, the outer dimensions of a jack device with the above structure can be made equal to the outer dimensions of a conventional jack device while preventing short circuit of the two contact pieces. That is, the jack device of the present invention can be used for a conventional plug without changing its length.